package org.apache.lucene.search;

/**
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

import java.io.IOException;
import java.util.BitSet;

import org.apache.lucene.store.Directory;
import org.apache.lucene.document.Document;
import org.apache.lucene.index.IndexReader;
import org.apache.lucene.index.Term;
import org.apache.lucene.util.PriorityQueue;

/** A {@link HitCollector} implementation that collects the top-scoring
 * documents, returning them as a {@link TopDocs}.  This is used by {@link
 * IndexSearcher} to implement {@link TopDocs}-based search.
 *
 * <p>This may be extended, overriding the collect method to, e.g.,
 * conditionally invoke <code>super()</code> in order to filter which
 * documents are collected.
 **/
public class TopDocCollector extends HitCollector {
    private int numHits;
    private float minScore = 0.0f;

    int totalHits;
    PriorityQueue hq;

    /** Construct to collect a given number of hits.
     * @param numHits the maximum number of hits to collect
     */
    public TopDocCollector(int numHits) {
        this(numHits, new HitQueue(numHits));
    }

    TopDocCollector(int numHits, PriorityQueue hq) {
        this.numHits = numHits;
        this.hq = hq;
    }

    // javadoc inherited
    public void collect(int doc, float score) {
        if (score > 0.0f) {
            totalHits++;
            if (hq.size() < numHits || score >= minScore) {
                hq.insert(new ScoreDoc(doc, score));
                minScore = ((ScoreDoc) hq.top()).score; // maintain minScore
            }
        }
    }

    /** The total number of documents that matched this query. */
    public int getTotalHits() {
        return totalHits;
    }

    /** The top-scoring hits. */
    public TopDocs topDocs() {
        ScoreDoc[] scoreDocs = new ScoreDoc[hq.size()];
        for (int i = hq.size() - 1; i >= 0; i--) // put docs in array
            scoreDocs[i] = (ScoreDoc) hq.pop();

        float maxScore = (totalHits == 0) ? Float.NEGATIVE_INFINITY : scoreDocs[0].score;

        return new TopDocs(totalHits, scoreDocs, maxScore);
    }
}
